Advanced composite materials have been developed to where production engineering now is being phased into a heretofore purely developmental engineering effort. This integration of engineering efforts is exposing new needs for improvements in advanced composite materials. Now emphasis is being placed on the economic efficiencies of the processes used for manufacturing composites and, as these materials are being incorporated into hardware structural designs, new processes are being sought. Two major deficiencies have become apparent with regard to the state-of-the-art high performance epoxy resin systems. The first problem is the high amount of resin flow during molding which can be as much as 50 percent of the original resin content. High resin flow may be attributed to the fact that some epoxy resins are liquid and inherently possess a high resin flow during molding, while other epoxy resins which require a solvent, retain the solvent during manufacture of the resinous article. Sometimes, during processing, the resin flow is deliberately employed to wash out the retained solvent and other gaseous matter.
The second major deficiency with respect to epoxy resins is the requirement for use of autoclaves to provide the essential pressure necessary for the consolidation of complex parts. This requirement for pressure greatly limits the number of vendors capable of handling the high performance materials.
Polybutadiene resins, on the other hand, have been of considerable interest for many years because of their excellent chemical stability and good physical properties.
U.S. Pat. No. 2,586,594 taught a tough, chemically stable resin coating could be applied to a substrate by the application of the liquid polybutadiene and the subsequent peroxide cure. While this system offered the benefit of good physical and chemical properties, the liquid polybutadiene require specialized and skillful handling techniques. Further development improved this system, but the handling and workability problems were never completely overcome. More recently, U.S. Pat. No. 3,431,235 offered a solution to the problems of workability and handling by the formation of an intermediate elastomeric material which may be handled and worked without special equipment and requirements. Thus, the polymer compounder who is equipped to handle viscous and tacky material, formulates a resin composition according to the fabricators' specifications and cures the material to an intermediate elastomeric stage. The fabricator then produces the final product without the necessity of special equipment to handle viscous, tacky polymeric materials. While U.S. Pat. No. 3,431,235 taught the solution to many of the problems associated with thermoset polydiene resins, when chain extended with high molecular weight epoxy resins, the nonpolar polybutadiene resins, upon curing, had the inherent problem of exuding the uncured polar epoxy resins. This produced a tacky nonhomogeneous polymer having unusable properties.